This project will take a top-down view of a pathophysiological function (opiate addiction) to develop a network-based understanding of the changes that occur during the addicted state. The project will extend previous network representation of neuronal signaling networks by developing networks where spatial representation is included and experimentally analyzed. Throughout history, opiates have been among the most widely consumed illicit drugs in the world (1). Repeated opiate use is known to produce tolerance, physical dependence, and addiction, which limit their long-term therapeutic use and can contribute to opiate abuse. Addiction is a chronically relapsing disorder characterized by the compulsive seeking and taking of a drug despite adverse consequences, as well as the emergence of a negative emotional state when access to the drug is prevented (2). In general, addictive drugs are thought to stimulate a reward pathway in the brain, which consists primarily of a circuit between the nucleus accumbens (NAc), ventral tec mental area (VTA), and the prefrontal cortex (PFC) (Figure 1). A number of studies have suggested that the mesolimbic dopaminergic system projecting from the VTA to the NAc is necessary for the initiation of opiate reward (3, 4). Several studies have shown that morphine-mediated inhibition of GABA release from the VTA leads to an increase in dopamine release at the NAc (5-7). This in turn leads to activation of dopamine receptors at the NAc. The morphine-induced reward can be blocked by direct administration of D1 dopamine receptor antagonists into the NAc (8, 9) demonstrating that the rewarding effects of opioids are dependent on DA neural transmission within the mesolimbic system and suggest a critical role for NAc in the mediation of both motivational effects. The overall goal of this project is to understand how the opiate addicted state in animals contributes to the alternation of the cell signaling network and how this alteration affects the spatial dynamics of G protein pathways in neurons from NAc (ventral striatum). The underlying hypothesis based on our preliminary data is that, chronic opiate treatment leads to reconfiguration of the regulatory loops within signaling networks. In this project, we will focus on NAc to examine the regulatory loops within signaling networks to determine how they are reconfigured during opiate addiction.